Experimental evidence of the molecular and macroscopic origins of circular dichroism in chiral metal-halide networks

Experimental evidence of the molecular and macroscopic origins of circular dichroism in chiral metal-halide networks | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Experimental evidence of the molecular and macroscopic origins of circular dichroism in chiral metal-halide networks Alexandre Abhervé This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3856748/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 25 May, 2024 Read the published version in Advanced Optical Materials → Version 1 posted You are reading this latest preprint version Abstract Clockwise or counter-clockwise spin coating? In the current hot research topic of chiral metal-halide semiconductors, several investigations have been undertaken in order to reveal their natural optical activity and have reported dissymmetry factors ( g abs ) for thin films of many hybrid compounds, usually without considering the macroscopic anisotropies inherent to solid-state samples. Yet, CD in the solid state can be strongly modulated by the co-existence of linear dichroism (LD) and linear birefringence (LB). Theoretical studies recently revealed the importance of such macroscopic interferences in the CD response of solid-state samples, often referred as symmetric (sLDLB) and antisymmetric (aLDLB) effects. Based on the newly synthesized one-dimensional lead-halide networks of formula ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 , an experimental method to accurately discriminate between CD, sLDLB and aLDLB in chiral metal-halide networks is here presented. The main experimental conditions influencing sLDLB and aLDLB amplitude are also highlighted, such as the concentration of the precursor solution and the spin-coating rotation direction, finally providing a complete experimental guide for the forthcoming chiroptical investigations of such important family of chiral hybrid materials. Physical sciences/Chemistry/Materials chemistry/Optical materials Physical sciences/Materials science/Materials for devices/Electronic devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The recent development of chiral metal-halide semiconductors, such as chiral perovskites, allowed the characterization of their chiroptical properties by circular dichroism (CD), circularly polarized luminescence (CPL) and non-linear optics such as CD-dependent single-harmonic generation (SHG-CD). Based on the first results reported in the last six years, some comparative studies tried to evaluate the potential of this class of materials for chiroptical applications. It appeared that one-dimensional (1D) networks presented g abs factors of between 10 − 3 – 10 − 1 , one to two orders of magnitude higher than two-dimensional (2D) compounds (10 − 4 < g abs < 10 − 3 ). On the other hand, iodide-based compounds presented slightly higher g abs factors than bromide-based counterparts. However, these properties were evaluated either on bulk crystals or on crystalline thin films, most of the time without considering the macroscopic interferences that could modulate the CD response in solid-state samples. For instance, the record g abs factor of 0.04 reported in a 1D lead-iodide compound was actually obtained from a mixed composition of CD-active 1D ( S/R -NEA)PbI 3 and achiral 3D MAPbI 3 in the thin films, and neither the crystal structure or the co-assembly of the composite could be described. Furthermore, such samples were prepared starting with saturated precursor solutions which probably place the absorbance of the resulting thin films over the accuracy window of the CD spectroscopy technique. Controlling the purity and appropriateness of CD measurements is of paramount importance especially when dealing with solid-state samples with strong anisotropy. Indeed, it has been recently evidenced for organic molecules that linear dichroism (LD) and linear birefringence (LB) can strongly interact locally inside the thin film, and their contribution along the xy plane orthogonal to the light propagation can be detected as circular absorption. Considering LD and LB measured along the x - y axes, those measured along the bisectors of x - y axes (LD’ and LB’), the rotation angle of the sample around the optical axis ( θ ), together with some other constants associated to the detection system (residue birefringence α, azimuth angle a , P 2 x and P 2 y related to the transmittance of the detector), the experimentally measured CD signal can be expressed as $${CD}_{apparent}={CD}_{iso}+ \frac{1}{2}\left(L{D}^{{\prime }}\bullet LB-L{B}^{{\prime }}\bullet LD\right)+\left(-LD \text{cos}2\theta +L{D}^{{\prime }}\text{sin}2\theta \right)\text{sin}\alpha +({P}_{x}^{2}-{P}_{y}^{2})\text{sin}2a(-LB\text{cos}2\theta +L{B}^{{\prime }}\text{sin}2\theta )$$ 1 While the third and fourth terms in Eq. ( 1 ) result in small and easily identified artefacts, the second term in turn can be non-negligible or even predominant over genuine CD iso . This so-called LDLB effect involves pairs of non-parallel transition dipoles when projected in the plane orthogonal to the light propagation. Some experimental studies have demonstrated the macroscopic origins of LDLB and the possibility to isolate this effect from CD iso , by measuring the chiroptical response of the thin film in two different configurations, i.e. with the film pointing towards the light source (hereafter called “front position”) or toward the detector (“back position”). It was therefore described as antisymmetric with respect to the direction of light propagation. In parallel, the existence of another LDLB contribution was recently demonstrated when considering the helical stacking of the molecules along the light propagation direction. In this theoretical model by Tempelaar et al. (supported by experimental measurements on oligothiophene films), the total LDLB for two nondegenerate transition dipoles n and m could be expressed as $$LDLB={\xi }^{2}{\omega }^{2}\sum _{n,m}{S}_{n}{S}_{m}{V}_{n}{W}_{m}\left[\frac{1}{2}\text{sin}\left(2{\beta }_{nm}\right)- \frac{1}{3}\text{c}\text{o}\text{s}\left(2{\beta }_{nm}\right)\varphi \right]$$ 2 where ξ is a constant, ω , V n and W m are related to the energy of the transitions, S n and S m are the oscillator strengths, β nm the angle between the transition dipoles, and 𝜙 the twist angle between the first and last molecules in the stack (assuming that this angle has a value < < 1). The first term in Eq. ( 2 ) corresponds to the antisymmetric LDLB (hereafter denoted as aLDLB) and changes sign when flipping the sample as a result of the sine function. On the other hand, the second term mainly derives from the helical stacking 𝜙 of a single transition dipole along the light propagation direction, with a cosine function resulting in that case in the conservation of the sign upon sample flipping. Therefore, this term was referred as symmetric LDLB term and is hereafter denoted as sLDLB. All these macroscopic effects are expected to appear in highly crystalline films such as in the case of metal-halide semiconductors. However, the study of macroscopic interferences has been so far largely ignored in this family of materials. Very recently, H. Lu et al. faced this issue and have shown that aLDLB effects tend to increase when decreasing the dimensionality of the network. For instance, the apparent strong g abs factor of 0.1 measured in the first place in the zero-dimensional hybrid compound of formula ( R -MBA) 2 CuCl 4 was finally corrected and estimated at 2.5x10 − 3 since the original signal was strongly dominated by the aLDLB term. On the other hand, 1D networks were described to present similar contributions for both CD iso and aLDLB, while in 2D networks the measured signal is dominated by the CD iso term and no macroscopic interference could affect the values of the calculated g abs factors. For example, we very recently reported 2D lead-bromide networks based on the chiral S/R -2-hydroxy-propyl-1-ammonium ( S/R -HP1A) cations (Fig. 1 ), which presented a pure molecular CD with g abs of about ± 10 −4 and high spin polarization in the electron transport. In the present work, the CD characterization of new 1D lead-halide compounds of formula ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 is presented. Both compounds have similar crystal structures and only differ from the halide composition. Modulation of the thin film preparation conditions allows to evidence for the first time the presence of both CD, aLDLB and sLDLB in the family of hybrid metal-halide semiconductors. Based on these observations, it is possible to re-investigate the nature of the CD responses in previously reported compounds and to confirm the crucial role of hydrogen-bonding interactions in these organic-inorganic hybrid networks. Finally, a guide for accurately measuring the CD signature in these materials is provided, emphasizing the impact of halide composition, precursor concentration, thin film orientation during CD measurements and, unexpectedly, the direction of the rotation during the spin-coating process. Results Structures of ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 . Both bromide and iodide-based compounds crystallize in the non-centrosymmetric polar space group P 2 1 and are isostructural (Supplementary Table 1). Asymmetric units contain two cations and two PbX 3 units (Supplementary Fig. 1). The 1D network is based on double-chains of edge-sharing PbX 6 octahedra running along the crystallographic [100] direction. The polar axis is thus perpendicular to the propagation of the chains. Both independent octahedra are strongly distorted due to two different Pb–X bond distances (Supplementary Table 2). The shortest distance can be found between the metal center and the only terminal halide ion, while the longest distance point towards the center of the double-chain. Numerous N-H···X intermolecular interactions can be observed between cations and the terminal halides (Supplementary Fig. 2). On the other hand, the equatorial Pb–X bond distances have similar values (from 2.965(8) to 3.109(7) Å in ( S/R -HP1A)PbBr 3 and from 3.142(3) to 3.294(2) Å in ( S/R -HP1A)PbI 3 ). At first, the two pairs of edge-sharing octahedra from both enantiomeric compounds appear to share the same distortions and thus to be superimposable. However, by carefully looking in the equatorial plane, one can observe that the distribution of the bond distances values is clearly inverted between both enantiomeric compounds (Fig. 2 ). These mirror-image octahedra clearly highlight the chiral nature of the inorganic network. These compounds share many similarities such as the crystal structure, symmetry, nature of the metal and of the cation, distortion within the inorganic network, and only differ from each other by the nature of the halide. Therefore, they represent interesting materials to disclose the role of halide composition in the chiroptical properties. Thin films of ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 were prepared using the spin-coating method starting from DMF solution of pure crystalline samples, using the typical procedure previously reported (see Supplementary Information for experimental procedure). X-ray powder diffraction (XRPD) confirmed the phase and purity for both of the crystalline powders and in the thin films (Supplementary Figs. 3, 4 and 5). Chiroptical activity in ( S/R -HP1A)PbBr 3 . CD measurements in transmission mode were first performed by orienting the deposited film towards the light source (i.e. “front” position). The film was rotating along the optical axis and the CD response was measured for eight different azimuth angles θ , with a step of 45° between each measurement (Supplementary Fig. 6). Indeed, as previously described for organic molecules and coordination complexes, the small artefacts resulting from the third and fourth terms in Eq. ( 1 ) could be corrected by averaging the experimental values obtained at different θ angles. The same procedure was applied for the two enantiomeric compounds, and the averaged spectra are presented in Fig. 3 a. However, this first series of measurements gave no mirror-image spectra between ( S -HP1A)PbBr 3 and ( R -HP1A)PbBr 3 . Although the signals appear at similar wavelengths associated to the excitonic peak of the inorganic 1D network, with a sign inversion between the two enantiomeric compounds, the relative peak intensities were very different from each other. Since they were prepared starting from the same concentration of the precursor solution, thicknesses are expected to be very similar between both films. This is further confirmed by the relative absorbance, the same for both compounds (around 1.1). Using the formula g abs = CD / 32980 x Abs, it resulted in apparent dissymmetry factors of + 5.10 − 3 and − 1.10 − 2 for ( S -HP1A)PbBr 3 and ( R -HP1A)PbBr 3 , respectively. Very different results were obtained by flipping the sample and measuring the CD spectra in the “back” position (thin film oriented towards the detector), particularly in the case of ( R -HP1A)PbBr 3 for which the spectrum was almost inverted. These results confirm an important contribution of aLDLB effects in these crystalline films. Using the equations $${CD}_{iso}= \frac{1}{2}({CD}_{front}+{CD}_{back})$$ 3 $$aLDLB= \frac{1}{2}({CD}_{front}-{CD}_{back})$$ 4 it was possible to isolate the contribution of both terms (Fig. 3 b). As expected, the CD iso display mirror-image spectra between the two enantiomers. This finally allows to obtain accurate g abs factors of + 1.10 − 3 and − 1.10 − 3 for ( S -HP1A)PbBr 3 and ( R -HP1A)PbBr 3 , respectively. On the other hand, the aLDLB effects present different intensities between ( S -HP1A)PbBr 3 and ( R -HP1A)PbBr 3 , almost four times more intense in the latter. This stronger aLDLB explains the sign inversion in ( R -HP1A)PbBr 3 between CD front and CD back , which was not observed in the compound based on the S enantiomer. What is the rationale of the different aLDLB between the two enantiomers? In chiral molecules, while CD iso has a pure excitonic origin, aLDLB effects in turn are related to local anisotropy and the non-alignment of LD and LB transition dipoles. In the case of crystalline thin films particularly, as for metal-halide semiconductors, epitaxial growth can be strongly dependent on sample preparation. Therefore, at this step, we hypothesized the possible impact of the spin-coating procedure, precisely the direction of the rotation during deposition (clockwise vs counter-clockwise). Indeed, as any chiral molecule or assembly can be associated to a helical potential, this rotation direction is expected to influence the supramolecular assembly of two enantiomeric compounds to a varying extent. For many years, similar mechano-chiral effects have been demonstrated in (metal-)organic compounds. For example, J. M. Ribó et al. have shown the influence of rotatory evaporation of solutions for the chiral induction in porphyrin-based J-aggregates. In our typical spin-coated thin film fabrication procedure, the direction of rotation was configured clockwise. Therefore, a new series of thin films of ( S/R -HP1A)PbBr 3 was prepared, using the same precursor solutions and procedure but changing the rotation direction of the spin-coating (i.e. counter-clockwise). CD measurements for both front and back positions of the thin film strongly differ from the measurements performed with the clockwise preparation (Fig. 3 c). The same equations were used for the calculation of CD iso and aLDLB (Fig. 3 d). The obtained CD iso spectra mostly present the same shape and values as in the clockwise configuration, with a slight difference at lower energy (around 330 nm). This was expected due to the same chemical nature of the thin films. On the other hand, aLDLB was strongly affected by the clockwise/counter-clockwise parameter. It is rather difficult to quantitatively analyze the effect of the rotation on the intensity of these macroscopic effects, although it appeared from a large set of measurements that aLDLB tends to increase (in absolute value) for clockwise rotation compared to counter-clockwise in ( S -HP1A)PbBr 3 and tends to decrease in ( R -HP1A)PbBr 3 . XRPD measurements were performed for each compound and spin-coating configuration (Supplementary Fig. 7). The strong similarity between diffractograms, with almost no difference in peak relative intensities, shows that both chemical composition and crystal orientation inside the thin films remained unchanged with sample preparation. The absolute absorbance, which was the same for all compounds (Supplementary Fig. 8), also supports the thickness integrity among the series. On the other hand, optical microscopy images showed that the compounds presenting the strongest aLDLB signals have stronger roughness with the presence of larger crystal domains (Supplementary Fig. 9). Therefore, these results suggest that the synergy between the nature of the enantiomer and spin-coating rotation direction can influence the presence and size of crystal domains, and that larger the macroscopic anisotropy, stronger could be the aLDLB effects. Finally, starting the rotation before the deposition of the precursor solution could strongly decrease the strength of aLDLB in both films (Supplementary Fig. 10). These results reveal a real impact of the spin-coating parameters on the supramolecular assembly of chiral molecular materials. At this step, the presence of the symmetric LDLB term in the CD response has not yet been investigated. According to the theory of Tempelaar et al., sLDLB is invariant upon sample flipping and should in principle give bisignate profile of the spectrum, although it has a completely different origin than the Cotton effect in CD. 12 How to experimentally discriminate between genuine CD and sLDLB? As far as CD iso is concerned, the g abs factor should be independent to the film thickness l. Indeed, CD iso is a single-scattering event (scaling at l) and results in the thickness-independent g abs factor (CD normalized by absorbance). On the other hand, both aLDLB and sLDLB terms scale as l², since they are considered as double-scattering events. Therefore, the dissymmetry factors corresponding to aLDLB and sLDLB should linearly increase with sample thickness. Very recently, thickness-dependent CD studies were performed on thin films and KBr pellets of 1D and 2D chiral metal-halide compounds, however these measurements could only highlight the possible CD signal overload and absorbance saturation region. In order to confirm the presence or absence of sLDLB in ( S/R -HP1A)PbBr 3 , thin films of different thicknesses were prepared and characterized. Three different concentrations of the precursor solutions have been selected (0.2, 0.5 and 1.0 M based on the formula unit). For each concentration, thin films were prepared under both clockwise and counter-clockwise rotation and CD measurements were performed as previously described (Supplementary Fig. 11). According to surface profilometry measurements, these concentrations resulted in thin films of thicknesses of around 20, 60 and 130 nm (± 10 nm and average roughness of about 5 nm) for 0.2, 0.5 and 1.0 M concentration, respectively. Nevertheless, the apparent and genuine g abs factors were plot as function of the precursor solution concentrations for more accuracy (Fig. 4 ). The apparent dissymmetry factors can be strongly modulated due to the increasing contribution of aLDLB by increasing film thickness. Although a linear increase of the apparent g abs can be observed in some cases (as depicted by dashed lines in Fig. 4 ), the evolution of this factor doesn’t necessarily follow any function due to competing effect between CD iso and aLDLB (sometimes being opposite in sign at a given wavelength) and because the aLDLB can be affected by sample preparation, such as clockwise/counter-clockwise spin-coating rotation. After averaging CD front and CD back measurements, the obtained dissymmetry factors are the same for the three concentrations, confirming the genuine g abs values of about + 1.10 − 3 and − 1.10 − 3 for ( S -HP1A)PbBr 3 and ( R -HP1A)PbBr 3 , respectively. This constancy across the range of concentration also confirms the absence of thickness-dependent sLDLB in this series of thin films. It can be concluded that only CD iso and aLDLB are present in the bromide-based hybrid compounds. Finally, it appears that the aLDLB effects almost vanish for the lowest concentration of 0.2 M (Supplementary Fig. 11), proving that a pure molecular CD can be obtained under these conditions. Previous reports on solid-state CD of (metal-)organic materials reasonably described aLDLB as a reproducible effect rather than an experimental artefact, which allows to make use of these antisymmetric effects in practical devices. 9 However, it appears from the present measurements on ( S/R -HP1A)PbBr 3 that aLDLB can be strongly dependent on sample preparation, pointing out the importance of describing all the selected conditions of sample preparation before reporting any dissymmetry factor. It also reveals the possibility to modulate such conditions in order to optimize the CD iso /aLDLB ratio for the target application. Chiroptical activity in ( S/R -HP1A)PbI 3 . Lead-iodide compounds have been reported to exhibit the strongest dissymmetry factors, usually between three and five times the values obtained with the lead-bromide counterparts. In the present example, thin films of ( S/R -HP1A)PbI 3 prepared in the same conditions as ( S/R -HP1A)PbBr 3 exhibit much stronger CD signals (reaching a degree-scale), suggesting very high dissymmetry factors in the iodide-based compounds (Supplementary Fig. 12). With such amplitude of the CD signal, ( S/R -HP1A)PbI 3 appeared to be good candidates to perform CD measurements on a series of films prepared from a large range of concentrations of the precursor solution, ranging from 0.06 to 1.0 M based on the formula unit. At each concentration, the thin films presented an excitonic peak located at 417 nm (Fig. 5 a). The evolution of the absolute absorbance between samples indicates a linear increase of the film thickness with the concentration and further confirms the integrity of the chemical composition. This linear increase was also suggested based on profilometry surface measurements, with a thickness range estimated at between 20 nm (at 0.2 M) and 150 nm (1.0 M). The evolution in the chiroptical response across the series is less straightforward (Fig. 5 b). It thus appears important to verify the presence of artefacts, aLDLB and sLDLB effects for each concentration. For example, the thin film of ( S -HP1A)PbI 3 prepared from a 0.3 M precursor solution (absolute absorbance of around 0.8) shows a small but measurable azimuth angle dependence on both CD and LD values (Supplementary Fig. 13a-b). While the apparent g abs factor was first estimated at + 0.0229, this value was lowered to + 0.0227 after artefacts corrections. It shows that the thin film presents negligible LD. Finally, as confirmed by the superposition of CD measured in both front and back positions (Supplementary Fig. 13c), no measurable aLDLB contribution could be observed, thus confirming (at this step) the calculated g abs for such concentration. We can conclude that both artefacts and aLDLB can here be disregarded. For this reason, such iodide-based thin films don’t behave differently depending on the direction of the spin-coating rotation. Similarly, these corrections have been applied for all concentrations and both compounds, confirming the absence of measurable artefacts and aLDLB in the entire series of thin films. On the other hand, strong modulations both in shape and values of CD spectra could be observed for concentrations of 0.9 and 1.0 M, a clear indication of signal saturation for such high concentrations. In the range 0.06–0.8 M, a non-linear evolution of the maximum CD values was also observed, at the difference of the absolute absorbance (Fig. 5 c). Once normalized by the absorption, the values of dissymmetry factor at 417 nm were plot as function of concentration (Fig. 5 d). A strong evolution appeared, with an increase of g abs from ± 1.10 − 3 to ± 4.10 − 2 . The strong thickness-dependence suggests that the CD signals are dominated by sLDLB and co-exist with genuine CD iso in ( S/R -HP1A)PbI 3 thin films. Indeed, the g abs factors for the lowest thicknesses are calculated at + 1.10 − 3 and − 1.10 − 3 for ( S -HP1A)PbI 3 and ( R -HP1A)PbI 3 , respectively. These constant values obtained from 0.06 to 0.12 M suggest the pure molecular origin (CD iso ) of the CD response. At higher concentration, the g abs factor linearly increases until reaching a plateau at 0.6 M, supporting the presence of sLDLB which increases the dissymmetry factors up to ± 4.10 − 2 . The results also demonstrate the saturation of the CD signal at the highest thicknesses. Finally, it should be noted that very similar results were obtained by replacing the FTO substrates for glass substrates (Supplementary Fig. 14). Molecular origins of chiroptical activity. Surprisingly, the same values of genuine dissymmetry factors are obtained for both ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 thin films. It is rather contradictory with previous reports that highlighted the larger CD observed in iodide compounds compared to bromide compounds, although it can now be understood that such comparative studies possibly relied on uncomplete characterizations. In addition, such studies were lacking of isostructural bromide and iodide-based compounds. For these reasons, it was challenging to study the influence of chemical and structural properties in the chiroptical activity of metal-halide semiconductors. In this context, two different hypotheses were recently proposed. On the one hand, it was suggested that the higher CD responses observed in iodide networks compared to bromide networks could be explained based on the stronger spin-orbit coupling (SOC) in iodide compounds due to the smaller exciton binding energy. On the other hand, the fine modulation of the structure in nano-confined chiral perovskites suggested that the strength of hydrogen-bonding interactions between chiral cation and inorganic network could be considered as a key parameter for the chiroptical activity. 15 These two explanations on the origin of CD in metal-halide networks can be complementary. In the light of the present results, the hypothesis on intermolecular interactions seems to have more influence on the genuine CD, since the hydrogen-bonding contacts are strictly the same in both ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 . This has also been proposed to be at the origin of chirality transfer strength in a series of 2D chiral halide perovskites. Nevertheless, the first hypothesis on the influence of chirality-induced SOC cannot be disregarded, and could be envisaged to slightly influence the g abs values, even though it was not observed in the present compounds. Macroscopic effects on chiroptical activity. Despite the similar natural optical activity of both bromide and iodide-based hybrid compounds (with genuine g abs of ± 1.10 − 3 ), it clearly appears that the nature of the halide has a predominant role in the overall chiroptical response. Here, iodide-based compounds show an apparent dissymmetry factor of one order of magnitude higher than the bromide counterparts. As mentioned in the introduction, in the previous studies on chiroptical properties of metal-halide semiconductors, the nature of the halide (Br vs I) influenced the g abs values in a lesser extent. This was due to the fact that in both bromide and iodide-based 1D networks, a non-negligible aLDLB effect was observed and the calculated g abs values were comprised between 10 − 4 and 10 − 3 . To the best of our knowledge, no sLDLB effects were previously observed in chiral metal-halide semiconductors. Here, aLDLB effects could be observed only in ( S/R -HP1A)PbBr 3 , keeping the apparent dissymmetry factors in the range between 10 − 3 and 10 − 2 . On the other hand, the sLDLB effect observed in ( S/R -HP1A)PbI 3 resulted in an increase of this factor up to 4.10 − 2 . The reason for different linear contributions in two isostructural compounds may be explained by a different crystal growth of the thin films. ( R -HP1A)PbBr 3 and ( R -HP1A)PbI 3 thin films displayed very similar XRPD patterns, with the presence of only (0kl) peaks that confirmed the predominant deposition of the hybrid compound with the propagation direction of the 1D chain parallel to the substrate (Fig. 6 a, d). However, a stronger intensity of the peaks associated to the (002) and (040) planes could be observed in ( R -HP1A)PbBr 3 (highlighted in blue), as well as the presence of (051) and (071) peaks (highlighted in green). These additional peaks indicated a lower preferential orientation of the 1D chains in ( R -HP1A)PbBr 3 compared to ( R -HP1A)PbI 3 and could be at the origin of the very different thin film textures (Fig. 6 b, e). As mentioned in the chiroptical characterization of ( S/R -HP1A)PbBr 3 , the CD responses were associated to the presence of large crystal domains in the thin films (Fig. 6 c), with roughness that could be dependent on sample preparation. For ( S/R -HP1A)PbI 3 however, optical microscopy images of the thin films under unpolarized and polarized light confirm the absence of such large crystal domains and reveal an homogeneous texture of the films (Fig. 6 f) with a small and gradual increase of the roughness by increasing the film thickness (Supplementary Fig. 15). In conclusion, this huge difference of CD signal observed between thin films based on isostructural compounds and prepared under the same conditions couldn’t be explained based on the sole effect of SOC, but rather arises from different crystal growth and therefore different macroscopic effects inside the thin films, here leading in the case of bromide-based compounds to aLDLB effects due to large crystal domains, and to sLDLB in iodide-based compounds due to the twist angle between stacks of molecules, according to Tempelaar’s model. 12 The discussion can be extended to 2D metal-halide networks. As mentioned in the introduction, 1D networks have shown dissymmetry factors of more than one order of magnitude higher than 2D based compounds. For example, the 2D chiral compounds of formula ( S/R -HP1A)PbBr 4 displayed a g abs of ± 10 − 4 , 16 one order of magnitude lower that the 1D networks obtained starting from the same chiral cation. Such results were understood based on the increase of exciton broadening (due to lower quantum confinement) when increasing the dimensionality of the system. 13 However, on the basis of the new results obtained with ( S/R -HP1A)PbBr 3 and ( S/R -HP1A)PbI 3 , it is strongly envisaged that not only the SOC could influence the CD strength. In layered-based metal-halide networks, the strong preferential orientation on the substrate and optimal overlap between 2D layers naturally prevents crystal domains or twist angle between stacks, and therefore prevents the generation of (antisymmetric and symmetric) LDLB effects. On the other hand, it was observed for many years that 1D metal-halide compounds can show non-homogeneous deposition on surfaces, as observed in ( S/R -HP1A)PbBr 3 . Furthermore, the results obtained with ( S/R -HP1A)PbI 3 shed light on the strong effect due to the twist angle and non-homogeneous stacking of the molecules on the surface. Therefore, it is reasonable to conclude that 1D metal-halide networks are more interesting candidates than 2D compounds for the generation and modulation of CD strength by controlling aLDLB and sLDLB effects. Chiroptical activity measurements on metal-halide networks. The present results highlight the importance of measuring the chiroptical properties on thin films of various thicknesses and in various orientations for a same enantiomer. Indeed, it is crucial to analyze all possible macroscopic effects in order to perform a comparative study and conclude about the molecular origins of CD in metal-halide networks. Considering the new hypotheses, some compounds may therefore be re-investigated. For example, one of the first CD study of 1D lead-iodide networks reported a g abs factor of ± 0.02 (Supplementary Fig. 16). 7 Interestingly, the compounds of formula ( S/R -α-PEA)PbI 3 (α-PEA = α-phenylethylammonium) presented a different type of 1D network than in ( S/R -HP1A)PbI 3 (single-chain of face-sharing octahedra in ( S/R -α-PEA)PbI 3 , double-chain of edge-sharing octahedra in ( S/R -HP1A)PbI 3 ), but both compounds share similar apparent g abs factors at the given absorbance of 1 (± 0.02 in ( S/R -HP1A)PbI 3 at 0.4 M concentration). In the first place, these results could suggest that in 1D networks, the chiroptical properties would be influenced by the nature of the halide rather than the type of connectivity between metal-halide octahedra. By extension, one could anticipate a possible predominance of sLDLB in the CD responses of ( S/R -α-PEA)PbI 3 , such as it was observed in ( S/R -HP1A)PbI 3 . However, such assumptions will be strongly revised after a careful comparative study. Despite proper preparation conditions of ( S/R -α-PEA)PbI 3 thin films (precursor solution at 0.3 M, discarding any possible saturation of the CD signal) and the highly preferred orientation of the 1D chains as observed by XRPD, crystal domains were observed from optical microscopy images under polarized light. The authors also mentioned the possible presence of LD and LB due to a slight modulation of the CD response at different azimuth angle measurements. Still, the presence or absence of aLDLB couldn’t be confirmed since the measurements were performed for only one position (front or back) of the thin film. On the other hand, thickness-dependence measurements were not performed in order to discriminate between molecular CD and sLDLB. More recently, H. Lu et al. reported the crystal structure and solid-state CD of ( R -EBA)PbI 3 (EBA = ethylbenzylammonium), which is isostructural to ( S/R -α-PEA)PbI 3 due to the similarity in the cation structure (Supplementary Fig. 16a). 13 Interestingly, optical microscopy images of the film with crossed-linear polarizers revealed a similar aspect than in ( S/R -α-PEA)PbI 3 thin films with large crystal domains. The chiroptical activity of ( R -EBA)PbI 3 was analyzed in more details, showing strong aLDLB that could invert the CD response upon sample flipping. After extracting the aLDLB contribution from the apparent CD signal, the calculated g abs factor in ( R -EBA)PbI 3 was found at around − 7.10 − 4 at all thicknesses, demonstrating that the authors could disclose the pure molecular chirality of the material. It is therefore strongly envisaged that the strong CD responses obtained in the isostructural ( S/R -α-PEA)PbI 3 compounds were mainly altered by the presence of antisymmetric LDLB, at the difference of the predominant sLDLB in thin films of ( S/R -HP1A)PbI 3 . The observation of such different behaviors between two systems with similar chemical composition, which differ only by the organic cation used and the shape of the inorganic chain, further support the importance of hydrogen-bonding interactions between chiral organic cation and metal-halide network. A complete study on a large number of metal-halide networks would be necessary in order to reveal the relative contribution of molecular and macroscopic features on the ratio of CD/aLDLB/sLDLB, and to fully describe the polarization ability of 1D chiral metal-halide semiconductors. Through all these considerations, a guide for measuring CD of chiral metal-halide semiconductors with total accuracy can now be provided. To be fully validated, the g abs value must be reported for thin films prepared from non-saturated precursor solutions. The absence of artefacts must be controlled by performing measurements at various azimuth angles. More importantly, the presence/absence of aLDLB must be confirmed by flipping the film and comparing both front and back positions measurements. In the case of predominant aLDLB over CD iso , as observed in 1D lead-bromide networks, changing the direction of the rotation during the spin coating process can strongly modulate the CD iso /aLDLB ratio. This effect can be strongly minimized in the case of highly oriented thin films, which can be demonstrated by XRPD and the absence of crystal domains by polarized optical microscopy images. The CD iso or sLDLB nature of the chiroptical response can only be confirmed by the preparation and characterization of various thin films of different thicknesses, i.e., starting from different concentrations of the precursor solutions. Finally, to be fully reproducible, experimental procedures should describe all sample preparation parameters (duration of spin-coating, rpm speed), including the clockwise or counter-clockwise rotation during the spin-coating process. Discussion In conclusion, the synthesis and experimental chiroptical study of new lead-halide 1D networks could demonstrate the strong impact of macroscopic interferences in the solid-state CD signals. The possibility to synthesize isostructural compounds that only differ from the nature of the halide (Br vs I) was critical in order to observe the different linear effects and to reveal their macroscopic origins. It also allowed to disclose the pure molecular CD (CD iso ), which is inherently thickness-independent, from the antisymmetric and symmetric LDLB effects. The discrimination between aLDLB and sLDLB is straightforward since these effects differ from their variance and invariance upon sample flipping, respectively. Therefore, aLDLB contribution can be isolated after sample flipping, while performing the measurements on thin films of various thicknesses allows to discriminate between sLDLB and CD iso . A thickness-independent g abs factor proves the predominance of CD iso in the thin film. On the other hand, if a gradual increase of the dissymmetry factor is still observed after artefacts and aLDLB corrections, this demonstrates that the chiroptical properties are sLDLB in nature and originate from the helical stacking of a transition dipole. These results lead the possibility to re-investigate previous CD measurements of metal-halide networks. In combination with previous results, a trend in the chiroptical origins of metal-halide semiconductors can be observed, although it sometimes relies on uncomplete chiroptical measurements. This study demonstrates the importance of controlling the possible artefacts and LDLB contributions to get the real CD signature of a chiral metal-halide network. It also reveals the optimal preparation conditions as well as the characterization measurements necessary for a complete chiroptical study. Such methodology should be applied in a large range of hybrid networks in order to quantitatively analyze the impact of both exciton binding energy and intermolecular interactions on the chiroptical performances of this important family of hybrid materials. References Ahn, J.; Lee, E.; Tan, J.; Yang, W.; Kim, B. & Moon, J. A new class of chiral semiconductors: chiral-organic-molecule-incorporating organic-inorganic hybrid perovskites. Mater. Horiz. 4 , 851 (2017). Georgieva, Z. N.; Zhang, Z.; Zhang, P.; Bloom, B. P.; Beratan, D. N. & Waldeck, D. H. Ligand Coverage and Exciton Delocalization Control Chiral Imprinting in Perovskite Nanoplatelets. J. Phys. Chem. C 126 , 15986-15995 (2022). Chai, C.-Y.; Zhang, Q.-K.; Jing, C.-Q.; Han, X.-B.; Liu, C.-D.; Liang, B.-D.; Fan, C.-C.; Chen, Z.; Lei, X.-W.; Stroppa, A.; Agbaoye, R. O.; Adebayo, G. A.; Zhang, C.-F. & Zhang W. Single-Component White Circularly Polarized Luminescence in Chiral 1D Double-Chain Perovskites. Adv. Optical Mater. 11 , 2201996 (2023). Yuan, C. Li, X.; Semin, S.; Feng, Y.; Rasing, T. & Xu, J. Chiral Lead Halide Perovskite Nanowires for Second-Order Nonlinear Optics. Nano Lett. 18 , 5411-5417 (2018). Lu, H.; Valy Vardeny, Z. & Beard, M. C. Control of light, spin and charge with chiral metal halide semiconductors. Nat. Rev. Chem. 6 , 470-485 (2022). Dang, Y.; Liu, X.; Sun, Y.; Song, J.; Hu, W. & Tao, X. Bulk Chiral Halide Perovskite Single Crystals for Active Circular Dichroism and Circularly Polarized Luminescence. J. Phys. Chem. Lett. 11 , 1689-1696 (2020). Chen, C.; Gao, L.; Gao, W.; Ge, C.; Du, X.; Li, Z.; Yang, Y.; Niu, G. & Tang J. Circularly polarized light detection using chiral hybrid perovskite. Nat. Commun. 10 , 1927 (2019). Ishii, A. & Miyasaka, T. Direct detection of circular polarized light in helical 1D perovskite-based photodiode. Sci. Adv. 6 , eabd3274 (2020). Albano, G.; Pescitelli, G. & Di Bari, L. Reciprocal and Non-reciprocal Chiroptical Features in Thin Films of Organic Dyes. ChemNanoMat 8 , e202200219 (2022). Wolffs, M.; George, S. J.; Tomović, Ž.; Meskers, S. C. J.; Schenning, A. P. H. J. & Meijer, E. H. Macroscopic Origin of Circular Dichroism Effects by Alignment of Self-Assembled Fibers in Solution. Angew. Chem. Int. Ed. 46 , 8203-8205 (2007). Albano, G.; Lissia, M.; Pescitelli, G.; Aronica, L. A. & Di Bari, L. Chiroptical response inversion upon sample flipping in thin films of a chiral benzo[1,2- b :4,5- b ’]-dithiophene-based oligothiophene. Mater. Chem. Front. 1 , 2047-2056 (2017). Salij, A.; Goldsmith, R. H. & Tempelaar, R. Theory of Apparent Circular Dichroism Reveals the Origin of Inverted and Noninverted Chiroptical Response under Sample Flipping. J. Am. Chem. Soc. 143 , 21519-21531 (2021). Zhang, Z.; Wang, Z.; Sung, H. H.-Y.; Williams, I. D.; Yu, Z.-G. & Lu, H. Revealing the Intrinsic Chiroptical Activity in Chiral Metal-Halide Semiconductors. J. Am. Chem. Soc. 144 , 22242-22250 (2022). Hao, J.; Lu, H.; Mao, L.; Chen, X.; Beard, M. C. & Blackburn, J. L. Direct Detection of Circularly Polarized Light Using Chiral Copper Chloride−Carbon Nanotube Heterostructures. ACS Nano 15 , 7608-7617 (2021). Ma, S.; Jung, Y.-K.; Ahn, J.; Kyhm, J.; Tan, J.; Lee, H.; Jang, G.; Lee, C. U.; Walsh, A. & Moon, J. Elucidating the origin of chiroptical activity in chiral 2D perovskites through nano-confined growth. Nat. Commun. 13 , 3259 (2022). Abhervé, A.; Mercier, N.; Kumar, A.; Das, T. K.; Even, J.; Katan, C. & Kepenekian, M. Chirality Versus Symmetry: Electron’s Spin Selectivity in Nonpolar Chiral Lead-Bromide Perovskites. Adv. Mater. 2305784 (2023). Crusats, J.; El-Hachemi, Z. & Ribó, J. M. Hydrodynamic effects on chiral induction. Chem. Soc. Rev. 39 , 569-577 (2010). Ribó, J. M.; Crusats, J.; Sagués, F.; Claret, J. M. & Rubires, R. Chiral Sign Induction by Vortices During the Formation of Mesophases in Stirred Solutions. Science 292 , 2063-2066 (2001). Han, X.-B.; Wang, W.; Jin, M.-L.; Jing, C.-Q.; Liang, B.-D.; Chai, C.-Y.; Xiong, R.-G. & Zhang, W. Unveiling Chiral Perovskite CD Signal Scaling: Discerning Authentic and Counterfeit Signals through Sample-State Analysis. Anal. Chem. 95 , 16201-16209 (2023). Yu, Z.-G. Chirality-Induced Spin-Orbit Coupling, Spin Transport, and Natural Optical Activity in Hybrid Organic-Inorganic Perovskites. J. Phys. Chem. Lett. 11 , 8638-8646 (2020). Son, J.; Ma, S.; Jung, Y.-K.; Tan, J.; Jang, G.; Lee, C. U.; Lee, J.; Moon, S.; Jeong, W.; Walsh, A. & Moon, J. Unraveling chirality transfer mechanism by structural isomer-derived hydrogen bonding interaction in 2D chiral perovskite. Nat. Commun. 14 , 3124 (2023). Additional Declarations There is NO Competing Interest. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3856748","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":269978525,"identity":"db992177-e97f-4c30-a841-16b104203a1f","order_by":0,"name":"Alexandre Abhervé","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-3883-310X","institution":"CNRS","correspondingAuthor":true,"prefix":"","firstName":"Alexandre","middleName":"","lastName":"Abhervé","suffix":""}],"badges":[],"createdAt":"2024-01-12 11:35:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3856748/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3856748/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1002/adom.202400381","type":"published","date":"2024-05-25T07:40:33+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":52785859,"identity":"6304c9b1-b45e-49c3-a47a-bbeb8c7cc1bf","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":6382,"visible":true,"origin":"","legend":"\u003cp\u003eStructures of the chiral cations.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/03685f3857de12899123b486.png"},{"id":52786171,"identity":"233ba679-4a94-4aa5-8798-28ed0b349b38","added_by":"auto","created_at":"2024-03-15 18:49:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":393429,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCrystal structures of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS/R\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS/R\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbI\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e View of the unit cell and the two independent edge-sharing octahedra of (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e (left) and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e (right). \u003cstrong\u003eb\u003c/strong\u003e Same for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e. Color code: C (black), H (cyan), N (blue), O (red), Br (brown), I (pink), Pb (grey), PbBr\u003csub\u003e6\u003c/sub\u003e unit (grey octahedra), PbI\u003csub\u003e6\u003c/sub\u003e unit (violet octahedra). The longest and shortest apical Pb–X distances are represented in gold and brown, respectively. All equatorial Pb–X bonds are represented in different colors to highlight the chiral nature of the inorganic network.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/f8d73de4b11a23d044b51e82.png"},{"id":52785860,"identity":"b75836b4-51bf-4267-a7aa-468c34e9b621","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":127562,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCD of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (red lines) and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (blue lines).\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e CD measurements front and back configurations on spin-coated films prepared under clockwise rotation. \u003cstrong\u003eb\u003c/strong\u003e CD\u003csub\u003eiso\u003c/sub\u003e and LDLB calculated from experimental measurements in \u003cstrong\u003ea\u003c/strong\u003e. \u003cstrong\u003ec\u003c/strong\u003e, \u003cstrong\u003ed\u003c/strong\u003e Same for the thin films prepared under counter-clockwise rotation.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/adff27a6ec7a5f2db12048f1.png"},{"id":52785861,"identity":"aa8bff29-e995-4047-957a-63252d554c43","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":79533,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConcentration dependence of calculated \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eg\u003c/strong\u003e\u003c/em\u003e\u003csub\u003e\u003cstrong\u003eabs\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e factors at λ = 320 nm for (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS/R\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Values obtained for the clockwise spin-coating. A linear increase of apparent dissymmetry is observed for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e. \u003cstrong\u003eb\u003c/strong\u003e Values obtained for the counter-clockwise configuration. A linear increase of apparent dissymmetry is observed for (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e. In both cases, the calculated genuine factors are thickness-independent.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/d85c9f303d1da894ae701b3d.png"},{"id":52785862,"identity":"92c6a829-6d45-4c0a-964d-9d937053097b","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":269109,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCD study of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS/R\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbI\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. a\u003c/strong\u003e Absorbance and \u003cstrong\u003eb\u003c/strong\u003e CD measurements as a function of concentration of the precursor solution. \u003cstrong\u003ec\u003c/strong\u003e Concentration dependence of absorbance and CD values at 417 nm. \u003cstrong\u003ed\u003c/strong\u003e Concentration dependence of \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/ddefef7f581ff9799f3b6808.png"},{"id":52785864,"identity":"c70608c1-a125-480b-ba6e-4d9f6b15659d","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":558387,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThin film orientation study of (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbBr\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e and (\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eR\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-HP1A)PbI\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e XRPD diffraction patterns of (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e thin film with hkl planes indexation. \u003cstrong\u003eb\u003c/strong\u003e View of the crystal structure of (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e highlighting the preferential orientation of the 1D chains on the substrate. \u003cstrong\u003ec\u003c/strong\u003e Optical microscope image of the thin film under polarized light. \u003cstrong\u003ed\u003c/strong\u003e, \u003cstrong\u003ee\u003c/strong\u003e and \u003cstrong\u003ef\u003c/strong\u003e Same for (\u003cem\u003eR\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e. In \u003cstrong\u003eb\u003c/strong\u003e and \u003cstrong\u003ee\u003c/strong\u003e, the hkl plane corresponding to the main (0-1-1) peak is highlighted in red, the hkl planes observed in both compounds are highlighted in orange, and the hkl planes corresponding to the peaks observed for (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e are highlighted in green and blue.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/0a31c63c9816b1dfcd0ac653.png"},{"id":59713119,"identity":"72546710-e929-4e34-ba04-fb2d683372c0","added_by":"auto","created_at":"2024-07-05 07:40:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1902085,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/d75b609a-9a04-44e7-8705-b2c649be75c6.pdf"},{"id":52785865,"identity":"82e2565f-56b8-45c3-9ce2-113ec32d584b","added_by":"auto","created_at":"2024-03-15 18:40:21","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10217350,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"HP1APbX3SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-3856748/v1/1ebaf461ef4ae82aa6288465.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Experimental evidence of the molecular and macroscopic origins of circular dichroism in chiral metal-halide networks","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe recent development of chiral metal-halide semiconductors, such as chiral perovskites,\u003ca class=\"FNLink\" href=\"#Fn1\" id=\"#FNLinkFn1\"\u003e\u003c/a\u003e allowed the characterization of their chiroptical properties by circular dichroism (CD),\u003ca class=\"FNLink\" href=\"#Fn2\" id=\"#FNLinkFn2\"\u003e\u003c/a\u003e circularly polarized luminescence (CPL)\u003ca class=\"FNLink\" href=\"#Fn3\" id=\"#FNLinkFn3\"\u003e\u003c/a\u003e and non-linear optics such as CD-dependent single-harmonic generation (SHG-CD).\u003ca class=\"FNLink\" href=\"#Fn4\" id=\"#FNLinkFn4\"\u003e\u003c/a\u003e Based on the first results reported in the last six years, some comparative studies tried to evaluate the potential of this class of materials for chiroptical applications.\u003ca class=\"FNLink\" href=\"#Fn5\" id=\"#FNLinkFn5\"\u003e\u003c/a\u003e It appeared that one-dimensional (1D) networks presented \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors of between 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e \u0026ndash; 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, one to two orders of magnitude higher than two-dimensional (2D) compounds (10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e \u0026lt; \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e \u0026lt; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e). On the other hand, iodide-based compounds presented slightly higher \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors than bromide-based counterparts. However, these properties were evaluated either on bulk crystals\u003ca class=\"FNLink\" href=\"#Fn6\" id=\"#FNLinkFn6\"\u003e\u003c/a\u003e or on crystalline thin films,\u003ca class=\"FNLink\" href=\"#Fn7\" id=\"#FNLinkFn7\"\u003e\u003c/a\u003e most of the time without considering the macroscopic interferences that could modulate the CD response in solid-state samples. For instance, the record \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor of 0.04 reported in a 1D lead-iodide compound was actually obtained from a mixed composition of CD-active 1D (\u003cem\u003eS/R\u003c/em\u003e-NEA)PbI\u003csub\u003e3\u003c/sub\u003e and achiral 3D MAPbI\u003csub\u003e3\u003c/sub\u003e in the thin films, and neither the crystal structure or the co-assembly of the composite could be described.\u003ca class=\"FNLink\" href=\"#Fn8\" id=\"#FNLinkFn8\"\u003e\u003c/a\u003e Furthermore, such samples were prepared starting with saturated precursor solutions which probably place the absorbance of the resulting thin films over the accuracy window of the CD spectroscopy technique. Controlling the purity and appropriateness of CD measurements is of paramount importance especially when dealing with solid-state samples with strong anisotropy. Indeed, it has been recently evidenced for organic molecules that linear dichroism (LD) and linear birefringence (LB) can strongly interact locally inside the thin film, and their contribution along the \u003cem\u003exy\u003c/em\u003e plane orthogonal to the light propagation can be detected as circular absorption.\u003ca class=\"FNLink\" href=\"#Fn9\" id=\"#FNLinkFn9\"\u003e\u003c/a\u003e Considering LD and LB measured along the \u003cem\u003ex\u003c/em\u003e-\u003cem\u003ey\u003c/em\u003e axes, those measured along the bisectors of \u003cem\u003ex\u003c/em\u003e-\u003cem\u003ey\u003c/em\u003e axes (LD\u0026rsquo; and LB\u0026rsquo;), the rotation angle of the sample around the optical axis (\u003cem\u003eθ\u003c/em\u003e), together with some other constants associated to the detection system (residue birefringence α, azimuth angle \u003cem\u003ea\u003c/em\u003e, \u003cem\u003eP\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eP\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u003csub\u003e\u003cem\u003ey\u003c/em\u003e\u003c/sub\u003e related to the transmittance of the detector), the experimentally measured CD signal can be expressed as\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${CD}_{apparent}={CD}_{iso}+ \\frac{1}{2}\\left(L{D}^{{\\prime }}\\bullet LB-L{B}^{{\\prime }}\\bullet LD\\right)+\\left(-LD \\text{cos}2\\theta +L{D}^{{\\prime }}\\text{sin}2\\theta \\right)\\text{sin}\\alpha +({P}_{x}^{2}-{P}_{y}^{2})\\text{sin}2a(-LB\\text{cos}2\\theta +L{B}^{{\\prime }}\\text{sin}2\\theta )$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhile the third and fourth terms in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) result in small and easily identified artefacts, the second term in turn can be non-negligible or even predominant over genuine CD\u003csub\u003eiso\u003c/sub\u003e. This so-called LDLB effect involves pairs of non-parallel transition dipoles when projected in the plane orthogonal to the light propagation. Some experimental studies have demonstrated the macroscopic origins of LDLB\u003ca class=\"FNLink\" href=\"#Fn10\" id=\"#FNLinkFn10\"\u003e\u003c/a\u003e and the possibility to isolate this effect from CD\u003csub\u003eiso\u003c/sub\u003e,\u003ca class=\"FNLink\" href=\"#Fn11\" id=\"#FNLinkFn11\"\u003e\u003c/a\u003e by measuring the chiroptical response of the thin film in two different configurations, i.e. with the film pointing towards the light source (hereafter called \u0026ldquo;front position\u0026rdquo;) or toward the detector (\u0026ldquo;back position\u0026rdquo;). It was therefore described as antisymmetric with respect to the direction of light propagation. In parallel, the existence of another LDLB contribution was recently demonstrated when considering the helical stacking of the molecules along the light propagation direction.\u003ca class=\"FNLink\" href=\"#Fn12\" id=\"#FNLinkFn12\"\u003e\u003c/a\u003e In this theoretical model by Tempelaar et al. (supported by experimental measurements on oligothiophene films), the total LDLB for two nondegenerate transition dipoles \u003cem\u003en\u003c/em\u003e and \u003cem\u003em\u003c/em\u003e could be expressed as\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$LDLB={\\xi }^{2}{\\omega }^{2}\\sum _{n,m}{S}_{n}{S}_{m}{V}_{n}{W}_{m}\\left[\\frac{1}{2}\\text{sin}\\left(2{\\beta }_{nm}\\right)- \\frac{1}{3}\\text{c}\\text{o}\\text{s}\\left(2{\\beta }_{nm}\\right)\\varphi \\right]$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eξ\u003c/em\u003e is a constant, \u003cem\u003eω\u003c/em\u003e, \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e are related to the energy of the transitions, \u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e are the oscillator strengths, \u003cem\u003eβ\u003c/em\u003e\u003csub\u003e\u003cem\u003enm\u003c/em\u003e\u003c/sub\u003e the angle between the transition dipoles, and \u0026#120601; the twist angle between the first and last molecules in the stack (assuming that this angle has a value\u0026thinsp;\u0026lt;\u0026thinsp;\u0026lt;\u0026thinsp;1). The first term in Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) corresponds to the antisymmetric LDLB (hereafter denoted as aLDLB) and changes sign when flipping the sample as a result of the sine function. On the other hand, the second term mainly derives from the helical stacking \u0026#120601; of a single transition dipole along the light propagation direction, with a cosine function resulting in that case in the conservation of the sign upon sample flipping. Therefore, this term was referred as symmetric LDLB term and is hereafter denoted as sLDLB. All these macroscopic effects are expected to appear in highly crystalline films such as in the case of metal-halide semiconductors. However, the study of macroscopic interferences has been so far largely ignored in this family of materials. Very recently, H. Lu et al. faced this issue and have shown that aLDLB effects tend to increase when decreasing the dimensionality of the network.\u003ca class=\"FNLink\" href=\"#Fn13\" id=\"#FNLinkFn13\"\u003e\u003c/a\u003e For instance, the apparent strong \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor of 0.1 measured in the first place in the zero-dimensional hybrid compound of formula (\u003cem\u003eR\u003c/em\u003e-MBA)\u003csub\u003e2\u003c/sub\u003eCuCl\u003csub\u003e4\u003c/sub\u003e\u003ca class=\"FNLink\" href=\"#Fn14\" id=\"#FNLinkFn14\"\u003e\u003c/a\u003e was finally corrected and estimated at 2.5x10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e since the original signal was strongly dominated by the aLDLB term. On the other hand, 1D networks were described to present similar contributions for both CD\u003csub\u003eiso\u003c/sub\u003e and aLDLB, while in 2D networks the measured signal is dominated by the CD\u003csub\u003eiso\u003c/sub\u003e term and no macroscopic interference could affect the values of the calculated \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors.\u003ca class=\"FNLink\" href=\"#Fn15\" id=\"#FNLinkFn15\"\u003e\u003c/a\u003e For example, we very recently reported 2D lead-bromide networks based on the chiral \u003cem\u003eS/R\u003c/em\u003e-2-hydroxy-propyl-1-ammonium (\u003cem\u003eS/R\u003c/em\u003e-HP1A) cations (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which presented a pure molecular CD with \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e of about\u0026thinsp;\u0026plusmn;\u0026thinsp;10\u003csup\u003e\u0026minus;4\u003c/sup\u003e and high spin polarization in the electron transport.\u003ca class=\"FNLink\" href=\"#Fn16\" id=\"#FNLinkFn16\"\u003e\u003c/a\u003e In the present work, the CD characterization of new 1D lead-halide compounds of formula (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e is presented. Both compounds have similar crystal structures and only differ from the halide composition. Modulation of the thin film preparation conditions allows to evidence for the first time the presence of both CD, aLDLB and sLDLB in the family of hybrid metal-halide semiconductors. Based on these observations, it is possible to re-investigate the nature of the CD responses in previously reported compounds and to confirm the crucial role of hydrogen-bonding interactions in these organic-inorganic hybrid networks. Finally, a guide for accurately measuring the CD signature in these materials is provided, emphasizing the impact of halide composition, precursor concentration, thin film orientation during CD measurements and, unexpectedly, the direction of the rotation during the spin-coating process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cb\u003eStructures of (\u003c/b\u003e \u003cb\u003eS/R\u003c/b\u003e \u003cb\u003e-HP1A)PbBr\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e \u003cb\u003eand (\u003c/b\u003e\u003cb\u003eS/R\u003c/b\u003e\u003cb\u003e-HP1A)PbI\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e. Both bromide and iodide-based compounds crystallize in the non-centrosymmetric polar space group \u003cem\u003eP\u003c/em\u003e2\u003csub\u003e1\u003c/sub\u003e and are isostructural (Supplementary Table\u0026nbsp;1). Asymmetric units contain two cations and two PbX\u003csub\u003e3\u003c/sub\u003e units (Supplementary Fig.\u0026nbsp;1). The 1D network is based on double-chains of edge-sharing PbX\u003csub\u003e6\u003c/sub\u003e octahedra running along the crystallographic [100] direction. The polar axis is thus perpendicular to the propagation of the chains. Both independent octahedra are strongly distorted due to two different Pb\u0026ndash;X bond distances (Supplementary Table\u0026nbsp;2). The shortest distance can be found between the metal center and the only terminal halide ion, while the longest distance point towards the center of the double-chain. Numerous N-H\u0026middot;\u0026middot;\u0026middot;X intermolecular interactions can be observed between cations and the terminal halides (Supplementary Fig.\u0026nbsp;2). On the other hand, the equatorial Pb\u0026ndash;X bond distances have similar values (from 2.965(8) to 3.109(7) \u0026Aring; in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and from 3.142(3) to 3.294(2) \u0026Aring; in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e). At first, the two pairs of edge-sharing octahedra from both enantiomeric compounds appear to share the same distortions and thus to be superimposable. However, by carefully looking in the equatorial plane, one can observe that the distribution of the bond distances values is clearly inverted between both enantiomeric compounds (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These mirror-image octahedra clearly highlight the chiral nature of the inorganic network.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese compounds share many similarities such as the crystal structure, symmetry, nature of the metal and of the cation, distortion within the inorganic network, and only differ from each other by the nature of the halide. Therefore, they represent interesting materials to disclose the role of halide composition in the chiroptical properties. Thin films of (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e were prepared using the spin-coating method starting from DMF solution of pure crystalline samples, using the typical procedure previously reported (see Supplementary Information for experimental procedure). X-ray powder diffraction (XRPD) confirmed the phase and purity for both of the crystalline powders and in the thin films (Supplementary Figs.\u0026nbsp;3, 4 and 5).\u003c/p\u003e \u003cp\u003e \u003cb\u003eChiroptical activity in (\u003c/b\u003e \u003cb\u003eS/R\u003c/b\u003e \u003cb\u003e-HP1A)PbBr\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e. CD measurements in transmission mode were first performed by orienting the deposited film towards the light source (i.e. \u0026ldquo;front\u0026rdquo; position). The film was rotating along the optical axis and the CD response was measured for eight different azimuth angles \u003cem\u003eθ\u003c/em\u003e, with a step of 45\u0026deg; between each measurement (Supplementary Fig.\u0026nbsp;6). Indeed, as previously described for organic molecules and coordination complexes, the small artefacts resulting from the third and fourth terms in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) could be corrected by averaging the experimental values obtained at different \u003cem\u003eθ\u003c/em\u003e angles. The same procedure was applied for the two enantiomeric compounds, and the averaged spectra are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. However, this first series of measurements gave no mirror-image spectra between (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e. Although the signals appear at similar wavelengths associated to the excitonic peak of the inorganic 1D network, with a sign inversion between the two enantiomeric compounds, the relative peak intensities were very different from each other. Since they were prepared starting from the same concentration of the precursor solution, thicknesses are expected to be very similar between both films. This is further confirmed by the relative absorbance, the same for both compounds (around 1.1). Using the formula \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e = CD / 32980 x Abs, it resulted in apparent dissymmetry factors of +\u0026thinsp;5.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and \u0026minus;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, respectively. Very different results were obtained by flipping the sample and measuring the CD spectra in the \u0026ldquo;back\u0026rdquo; position (thin film oriented towards the detector), particularly in the case of (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e for which the spectrum was almost inverted. These results confirm an important contribution of aLDLB effects in these crystalline films. Using the equations\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${CD}_{iso}= \\frac{1}{2}({CD}_{front}+{CD}_{back})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$aLDLB= \\frac{1}{2}({CD}_{front}-{CD}_{back})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eit was possible to isolate the contribution of both terms (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). As expected, the CD\u003csub\u003eiso\u003c/sub\u003e display mirror-image spectra between the two enantiomers. This finally allows to obtain accurate \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors of +\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and \u0026minus;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, respectively. On the other hand, the aLDLB effects present different intensities between (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, almost four times more intense in the latter. This stronger aLDLB explains the sign inversion in (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e between CD\u003csub\u003efront\u003c/sub\u003e and CD\u003csub\u003eback\u003c/sub\u003e, which was not observed in the compound based on the \u003cem\u003eS\u003c/em\u003e enantiomer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWhat is the rationale of the different aLDLB between the two enantiomers? In chiral molecules, while CD\u003csub\u003eiso\u003c/sub\u003e has a pure excitonic origin, aLDLB effects in turn are related to local anisotropy and the non-alignment of LD and LB transition dipoles. In the case of crystalline thin films particularly, as for metal-halide semiconductors, epitaxial growth can be strongly dependent on sample preparation. Therefore, at this step, we hypothesized the possible impact of the spin-coating procedure, precisely the direction of the rotation during deposition (clockwise vs counter-clockwise). Indeed, as any chiral molecule or assembly can be associated to a helical potential, this rotation direction is expected to influence the supramolecular assembly of two enantiomeric compounds to a varying extent. For many years, similar mechano-chiral effects have been demonstrated in (metal-)organic compounds.\u003ca class=\"FNLink\" href=\"#Fn17\" id=\"#FNLinkFn17\"\u003e\u003c/a\u003e For example, J. M. Rib\u0026oacute; et al. have shown the influence of rotatory evaporation of solutions for the chiral induction in porphyrin-based J-aggregates.\u003ca class=\"FNLink\" href=\"#Fn18\" id=\"#FNLinkFn18\"\u003e\u003c/a\u003e In our typical spin-coated thin film fabrication procedure, the direction of rotation was configured clockwise. Therefore, a new series of thin films of (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e was prepared, using the same precursor solutions and procedure but changing the rotation direction of the spin-coating (i.e. counter-clockwise). CD measurements for both front and back positions of the thin film strongly differ from the measurements performed with the clockwise preparation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). The same equations were used for the calculation of CD\u003csub\u003eiso\u003c/sub\u003e and aLDLB (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The obtained CD\u003csub\u003eiso\u003c/sub\u003e spectra mostly present the same shape and values as in the clockwise configuration, with a slight difference at lower energy (around 330 nm). This was expected due to the same chemical nature of the thin films. On the other hand, aLDLB was strongly affected by the clockwise/counter-clockwise parameter. It is rather difficult to quantitatively analyze the effect of the rotation on the intensity of these macroscopic effects, although it appeared from a large set of measurements that aLDLB tends to increase (in absolute value) for clockwise rotation compared to counter-clockwise in (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and tends to decrease in (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e. XRPD measurements were performed for each compound and spin-coating configuration (Supplementary Fig.\u0026nbsp;7). The strong similarity between diffractograms, with almost no difference in peak relative intensities, shows that both chemical composition and crystal orientation inside the thin films remained unchanged with sample preparation. The absolute absorbance, which was the same for all compounds (Supplementary Fig.\u0026nbsp;8), also supports the thickness integrity among the series. On the other hand, optical microscopy images showed that the compounds presenting the strongest aLDLB signals have stronger roughness with the presence of larger crystal domains (Supplementary Fig.\u0026nbsp;9). Therefore, these results suggest that the synergy between the nature of the enantiomer and spin-coating rotation direction can influence the presence and size of crystal domains, and that larger the macroscopic anisotropy, stronger could be the aLDLB effects. Finally, starting the rotation before the deposition of the precursor solution could strongly decrease the strength of aLDLB in both films (Supplementary Fig.\u0026nbsp;10). These results reveal a real impact of the spin-coating parameters on the supramolecular assembly of chiral molecular materials.\u003c/p\u003e \u003cp\u003eAt this step, the presence of the symmetric LDLB term in the CD response has not yet been investigated. According to the theory of Tempelaar et al., sLDLB is invariant upon sample flipping and should in principle give bisignate profile of the spectrum, although it has a completely different origin than the Cotton effect in CD.\u003csup\u003e12\u003c/sup\u003e How to experimentally discriminate between genuine CD and sLDLB? As far as CD\u003csub\u003eiso\u003c/sub\u003e is concerned, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor should be independent to the film thickness l. Indeed, CD\u003csub\u003eiso\u003c/sub\u003e is a single-scattering event (scaling at l) and results in the thickness-independent \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor (CD normalized by absorbance). On the other hand, both aLDLB and sLDLB terms scale as l\u0026sup2;, since they are considered as double-scattering events. Therefore, the dissymmetry factors corresponding to aLDLB and sLDLB should linearly increase with sample thickness. Very recently, thickness-dependent CD studies were performed on thin films and KBr pellets of 1D and 2D chiral metal-halide compounds, however these measurements could only highlight the possible CD signal overload and absorbance saturation region.\u003ca class=\"FNLink\" href=\"#Fn19\" id=\"#FNLinkFn19\"\u003e\u003c/a\u003e In order to confirm the presence or absence of sLDLB in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, thin films of different thicknesses were prepared and characterized. Three different concentrations of the precursor solutions have been selected (0.2, 0.5 and 1.0 M based on the formula unit). For each concentration, thin films were prepared under both clockwise and counter-clockwise rotation and CD measurements were performed as previously described (Supplementary Fig.\u0026nbsp;11). According to surface profilometry measurements, these concentrations resulted in thin films of thicknesses of around 20, 60 and 130 nm (\u0026plusmn;\u0026thinsp;10 nm and average roughness of about 5 nm) for 0.2, 0.5 and 1.0 M concentration, respectively. Nevertheless, the apparent and genuine \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors were plot as function of the precursor solution concentrations for more accuracy (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The apparent dissymmetry factors can be strongly modulated due to the increasing contribution of aLDLB by increasing film thickness. Although a linear increase of the apparent \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e can be observed in some cases (as depicted by dashed lines in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), the evolution of this factor doesn\u0026rsquo;t necessarily follow any function due to competing effect between CD\u003csub\u003eiso\u003c/sub\u003e and aLDLB (sometimes being opposite in sign at a given wavelength) and because the aLDLB can be affected by sample preparation, such as clockwise/counter-clockwise spin-coating rotation. After averaging CD\u003csub\u003efront\u003c/sub\u003e and CD\u003csub\u003eback\u003c/sub\u003e measurements, the obtained dissymmetry factors are the same for the three concentrations, confirming the genuine \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e values of about\u0026thinsp;+\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and \u0026minus;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, respectively. This constancy across the range of concentration also confirms the absence of thickness-dependent sLDLB in this series of thin films. It can be concluded that only CD\u003csub\u003eiso\u003c/sub\u003e and aLDLB are present in the bromide-based hybrid compounds. Finally, it appears that the aLDLB effects almost vanish for the lowest concentration of 0.2 M (Supplementary Fig.\u0026nbsp;11), proving that a pure molecular CD can be obtained under these conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePrevious reports on solid-state CD of (metal-)organic materials reasonably described aLDLB as a reproducible effect rather than an experimental artefact, which allows to make use of these antisymmetric effects in practical devices.\u003csup\u003e9\u003c/sup\u003e However, it appears from the present measurements on (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e that aLDLB can be strongly dependent on sample preparation, pointing out the importance of describing all the selected conditions of sample preparation before reporting any dissymmetry factor. It also reveals the possibility to modulate such conditions in order to optimize the CD\u003csub\u003eiso\u003c/sub\u003e/aLDLB ratio for the target application.\u003c/p\u003e \u003cp\u003e \u003cb\u003eChiroptical activity in (\u003c/b\u003e \u003cb\u003eS/R\u003c/b\u003e \u003cb\u003e-HP1A)PbI\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003e. Lead-iodide compounds have been reported to exhibit the strongest dissymmetry factors, usually between three and five times the values obtained with the lead-bromide counterparts. In the present example, thin films of (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e prepared in the same conditions as (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e exhibit much stronger CD signals (reaching a degree-scale), suggesting very high dissymmetry factors in the iodide-based compounds (Supplementary Fig.\u0026nbsp;12). With such amplitude of the CD signal, (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e appeared to be good candidates to perform CD measurements on a series of films prepared from a large range of concentrations of the precursor solution, ranging from 0.06 to 1.0 M based on the formula unit. At each concentration, the thin films presented an excitonic peak located at 417 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The evolution of the absolute absorbance between samples indicates a linear increase of the film thickness with the concentration and further confirms the integrity of the chemical composition. This linear increase was also suggested based on profilometry surface measurements, with a thickness range estimated at between 20 nm (at 0.2 M) and 150 nm (1.0 M). The evolution in the chiroptical response across the series is less straightforward (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). It thus appears important to verify the presence of artefacts, aLDLB and sLDLB effects for each concentration.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor example, the thin film of (\u003cem\u003eS\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e prepared from a 0.3 M precursor solution (absolute absorbance of around 0.8) shows a small but measurable azimuth angle dependence on both CD and LD values (Supplementary Fig.\u0026nbsp;13a-b). While the apparent \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor was first estimated at +\u0026thinsp;0.0229, this value was lowered to +\u0026thinsp;0.0227 after artefacts corrections. It shows that the thin film presents negligible LD. Finally, as confirmed by the superposition of CD measured in both front and back positions (Supplementary Fig.\u0026nbsp;13c), no measurable aLDLB contribution could be observed, thus confirming (at this step) the calculated \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e for such concentration. We can conclude that both artefacts and aLDLB can here be disregarded. For this reason, such iodide-based thin films don\u0026rsquo;t behave differently depending on the direction of the spin-coating rotation. Similarly, these corrections have been applied for all concentrations and both compounds, confirming the absence of measurable artefacts and aLDLB in the entire series of thin films. On the other hand, strong modulations both in shape and values of CD spectra could be observed for concentrations of 0.9 and 1.0 M, a clear indication of signal saturation for such high concentrations. In the range 0.06\u0026ndash;0.8 M, a non-linear evolution of the maximum CD values was also observed, at the difference of the absolute absorbance (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Once normalized by the absorption, the values of dissymmetry factor at 417 nm were plot as function of concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). A strong evolution appeared, with an increase of \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e from \u0026plusmn;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e to \u0026plusmn;\u0026thinsp;4.10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The strong thickness-dependence suggests that the CD signals are dominated by sLDLB and co-exist with genuine CD\u003csub\u003eiso\u003c/sub\u003e in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e thin films. Indeed, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors for the lowest thicknesses are calculated at +\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and \u0026minus;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e for (\u003cem\u003eS\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e, respectively. These constant values obtained from 0.06 to 0.12 M suggest the pure molecular origin (CD\u003csub\u003eiso\u003c/sub\u003e) of the CD response. At higher concentration, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor linearly increases until reaching a plateau at 0.6 M, supporting the presence of sLDLB which increases the dissymmetry factors up to \u0026plusmn;\u0026thinsp;4.10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The results also demonstrate the saturation of the CD signal at the highest thicknesses. Finally, it should be noted that very similar results were obtained by replacing the FTO substrates for glass substrates (Supplementary Fig.\u0026nbsp;14).\u003c/p\u003e \u003cp\u003e \u003cb\u003eMolecular origins of chiroptical activity.\u003c/b\u003e Surprisingly, the same values of genuine dissymmetry factors are obtained for both (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e thin films. It is rather contradictory with previous reports that highlighted the larger CD observed in iodide compounds compared to bromide compounds, although it can now be understood that such comparative studies possibly relied on uncomplete characterizations. In addition, such studies were lacking of isostructural bromide and iodide-based compounds. For these reasons, it was challenging to study the influence of chemical and structural properties in the chiroptical activity of metal-halide semiconductors. In this context, two different hypotheses were recently proposed. On the one hand, it was suggested that the higher CD responses observed in iodide networks compared to bromide networks could be explained based on the stronger spin-orbit coupling (SOC) in iodide compounds due to the smaller exciton binding energy.\u003ca class=\"FNLink\" href=\"#Fn20\" id=\"#FNLinkFn20\"\u003e\u003c/a\u003e On the other hand, the fine modulation of the structure in nano-confined chiral perovskites suggested that the strength of hydrogen-bonding interactions between chiral cation and inorganic network could be considered as a key parameter for the chiroptical activity.\u003csup\u003e15\u003c/sup\u003e These two explanations on the origin of CD in metal-halide networks can be complementary. In the light of the present results, the hypothesis on intermolecular interactions seems to have more influence on the genuine CD, since the hydrogen-bonding contacts are strictly the same in both (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e. This has also been proposed to be at the origin of chirality transfer strength in a series of 2D chiral halide perovskites.\u003ca class=\"FNLink\" href=\"#Fn21\" id=\"#FNLinkFn21\"\u003e\u003c/a\u003e Nevertheless, the first hypothesis on the influence of chirality-induced SOC cannot be disregarded, and could be envisaged to slightly influence the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e values, even though it was not observed in the present compounds.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMacroscopic effects on chiroptical activity.\u003c/b\u003e Despite the similar natural optical activity of both bromide and iodide-based hybrid compounds (with genuine \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e of \u0026plusmn;\u0026thinsp;1.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), it clearly appears that the nature of the halide has a predominant role in the overall chiroptical response. Here, iodide-based compounds show an apparent dissymmetry factor of one order of magnitude higher than the bromide counterparts. As mentioned in the introduction, in the previous studies on chiroptical properties of metal-halide semiconductors, the nature of the halide (Br \u003cem\u003evs\u003c/em\u003e I) influenced the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e values in a lesser extent. This was due to the fact that in both bromide and iodide-based 1D networks, a non-negligible aLDLB effect was observed and the calculated \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e values were comprised between 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e and 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e. To the best of our knowledge, no sLDLB effects were previously observed in chiral metal-halide semiconductors. Here, aLDLB effects could be observed only in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, keeping the apparent dissymmetry factors in the range between 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. On the other hand, the sLDLB effect observed in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e resulted in an increase of this factor up to 4.10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The reason for different linear contributions in two isostructural compounds may be explained by a different crystal growth of the thin films. (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eR\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e thin films displayed very similar XRPD patterns, with the presence of only (0kl) peaks that confirmed the predominant deposition of the hybrid compound with the propagation direction of the 1D chain parallel to the substrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, d). However, a stronger intensity of the peaks associated to the (002) and (040) planes could be observed in (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e (highlighted in blue), as well as the presence of (051) and (071) peaks (highlighted in green). These additional peaks indicated a lower preferential orientation of the 1D chains in (\u003cem\u003eR\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e compared to (\u003cem\u003eR\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e and could be at the origin of the very different thin film textures (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, e). As mentioned in the chiroptical characterization of (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e, the CD responses were associated to the presence of large crystal domains in the thin films (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec), with roughness that could be dependent on sample preparation. For (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e however, optical microscopy images of the thin films under unpolarized and polarized light confirm the absence of such large crystal domains and reveal an homogeneous texture of the films (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef) with a small and gradual increase of the roughness by increasing the film thickness (Supplementary Fig.\u0026nbsp;15). In conclusion, this huge difference of CD signal observed between thin films based on isostructural compounds and prepared under the same conditions couldn\u0026rsquo;t be explained based on the sole effect of SOC, but rather arises from different crystal growth and therefore different macroscopic effects inside the thin films, here leading in the case of bromide-based compounds to aLDLB effects due to large crystal domains, and to sLDLB in iodide-based compounds due to the twist angle between stacks of molecules, according to Tempelaar\u0026rsquo;s model.\u003csup\u003e12\u003c/sup\u003e The discussion can be extended to 2D metal-halide networks. As mentioned in the introduction, 1D networks have shown dissymmetry factors of more than one order of magnitude higher than 2D based compounds. For example, the 2D chiral compounds of formula (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e4\u003c/sub\u003e displayed a \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e of \u0026plusmn;\u0026thinsp;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e,\u003csup\u003e16\u003c/sup\u003e one order of magnitude lower that the 1D networks obtained starting from the same chiral cation. Such results were understood based on the increase of exciton broadening (due to lower quantum confinement) when increasing the dimensionality of the system.\u003csup\u003e13\u003c/sup\u003e However, on the basis of the new results obtained with (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e, it is strongly envisaged that not only the SOC could influence the CD strength. In layered-based metal-halide networks, the strong preferential orientation on the substrate and optimal overlap between 2D layers naturally prevents crystal domains or twist angle between stacks, and therefore prevents the generation of (antisymmetric and symmetric) LDLB effects. On the other hand, it was observed for many years that 1D metal-halide compounds can show non-homogeneous deposition on surfaces, as observed in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e. Furthermore, the results obtained with (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e shed light on the strong effect due to the twist angle and non-homogeneous stacking of the molecules on the surface. Therefore, it is reasonable to conclude that 1D metal-halide networks are more interesting candidates than 2D compounds for the generation and modulation of CD strength by controlling aLDLB and sLDLB effects.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eChiroptical activity measurements on metal-halide networks.\u003c/b\u003e The present results highlight the importance of measuring the chiroptical properties on thin films of various thicknesses and in various orientations for a same enantiomer. Indeed, it is crucial to analyze all possible macroscopic effects in order to perform a comparative study and conclude about the molecular origins of CD in metal-halide networks. Considering the new hypotheses, some compounds may therefore be re-investigated. For example, one of the first CD study of 1D lead-iodide networks reported a \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor of \u0026plusmn;\u0026thinsp;0.02 (Supplementary Fig.\u0026nbsp;16).\u003csup\u003e7\u003c/sup\u003e Interestingly, the compounds of formula (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e (α-PEA\u0026thinsp;=\u0026thinsp;α-phenylethylammonium) presented a different type of 1D network than in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e (single-chain of face-sharing octahedra in (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e, double-chain of edge-sharing octahedra in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e), but both compounds share similar apparent \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factors at the given absorbance of 1 (\u0026plusmn;\u0026thinsp;0.02 in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e at 0.4 M concentration). In the first place, these results could suggest that in 1D networks, the chiroptical properties would be influenced by the nature of the halide rather than the type of connectivity between metal-halide octahedra. By extension, one could anticipate a possible predominance of sLDLB in the CD responses of (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e, such as it was observed in (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e. However, such assumptions will be strongly revised after a careful comparative study. Despite proper preparation conditions of (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e thin films (precursor solution at 0.3 M, discarding any possible saturation of the CD signal) and the highly preferred orientation of the 1D chains as observed by XRPD, crystal domains were observed from optical microscopy images under polarized light. The authors also mentioned the possible presence of LD and LB due to a slight modulation of the CD response at different azimuth angle measurements. Still, the presence or absence of aLDLB couldn\u0026rsquo;t be confirmed since the measurements were performed for only one position (front or back) of the thin film. On the other hand, thickness-dependence measurements were not performed in order to discriminate between molecular CD and sLDLB. More recently, H. Lu et al. reported the crystal structure and solid-state CD of (\u003cem\u003eR\u003c/em\u003e-EBA)PbI\u003csub\u003e3\u003c/sub\u003e (EBA\u0026thinsp;=\u0026thinsp;ethylbenzylammonium), which is isostructural to (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e due to the similarity in the cation structure (Supplementary Fig.\u0026nbsp;16a).\u003csup\u003e13\u003c/sup\u003e Interestingly, optical microscopy images of the film with crossed-linear polarizers revealed a similar aspect than in (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e thin films with large crystal domains. The chiroptical activity of (\u003cem\u003eR\u003c/em\u003e-EBA)PbI\u003csub\u003e3\u003c/sub\u003e was analyzed in more details, showing strong aLDLB that could invert the CD response upon sample flipping. After extracting the aLDLB contribution from the apparent CD signal, the calculated \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor in (\u003cem\u003eR\u003c/em\u003e-EBA)PbI\u003csub\u003e3\u003c/sub\u003e was found at around \u0026minus;\u0026thinsp;7.10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e at all thicknesses, demonstrating that the authors could disclose the pure molecular chirality of the material. It is therefore strongly envisaged that the strong CD responses obtained in the isostructural (\u003cem\u003eS/R\u003c/em\u003e-α-PEA)PbI\u003csub\u003e3\u003c/sub\u003e compounds were mainly altered by the presence of antisymmetric LDLB, at the difference of the predominant sLDLB in thin films of (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e. The observation of such different behaviors between two systems with similar chemical composition, which differ only by the organic cation used and the shape of the inorganic chain, further support the importance of hydrogen-bonding interactions between chiral organic cation and metal-halide network. A complete study on a large number of metal-halide networks would be necessary in order to reveal the relative contribution of molecular and macroscopic features on the ratio of CD/aLDLB/sLDLB, and to fully describe the polarization ability of 1D chiral metal-halide semiconductors.\u003c/p\u003e \u003cp\u003eThrough all these considerations, a guide for measuring CD of chiral metal-halide semiconductors with total accuracy can now be provided. To be fully validated, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e value must be reported for thin films prepared from non-saturated precursor solutions. The absence of artefacts must be controlled by performing measurements at various azimuth angles. More importantly, the presence/absence of aLDLB must be confirmed by flipping the film and comparing both front and back positions measurements. In the case of predominant aLDLB over CD\u003csub\u003eiso\u003c/sub\u003e, as observed in 1D lead-bromide networks, changing the direction of the rotation during the spin coating process can strongly modulate the CD\u003csub\u003eiso\u003c/sub\u003e/aLDLB ratio. This effect can be strongly minimized in the case of highly oriented thin films, which can be demonstrated by XRPD and the absence of crystal domains by polarized optical microscopy images. The CD\u003csub\u003eiso\u003c/sub\u003e or sLDLB nature of the chiroptical response can only be confirmed by the preparation and characterization of various thin films of different thicknesses, i.e., starting from different concentrations of the precursor solutions. Finally, to be fully reproducible, experimental procedures should describe all sample preparation parameters (duration of spin-coating, rpm speed), including the clockwise or counter-clockwise rotation during the spin-coating process.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn conclusion, the synthesis and experimental chiroptical study of new lead-halide 1D networks could demonstrate the strong impact of macroscopic interferences in the solid-state CD signals. The possibility to synthesize isostructural compounds that only differ from the nature of the halide (Br vs I) was critical in order to observe the different linear effects and to reveal their macroscopic origins. It also allowed to disclose the pure molecular CD (CD\u003csub\u003eiso\u003c/sub\u003e), which is inherently thickness-independent, from the antisymmetric and symmetric LDLB effects. The discrimination between aLDLB and sLDLB is straightforward since these effects differ from their variance and invariance upon sample flipping, respectively. Therefore, aLDLB contribution can be isolated after sample flipping, while performing the measurements on thin films of various thicknesses allows to discriminate between sLDLB and CD\u003csub\u003eiso\u003c/sub\u003e. A thickness-independent \u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e factor proves the predominance of CD\u003csub\u003eiso\u003c/sub\u003e in the thin film. On the other hand, if a gradual increase of the dissymmetry factor is still observed after artefacts and aLDLB corrections, this demonstrates that the chiroptical properties are sLDLB in nature and originate from the helical stacking of a transition dipole. These results lead the possibility to re-investigate previous CD measurements of metal-halide networks. In combination with previous results, a trend in the chiroptical origins of metal-halide semiconductors can be observed, although it sometimes relies on uncomplete chiroptical measurements. This study demonstrates the importance of controlling the possible artefacts and LDLB contributions to get the real CD signature of a chiral metal-halide network. It also reveals the optimal preparation conditions as well as the characterization measurements necessary for a complete chiroptical study. Such methodology should be applied in a large range of hybrid networks in order to quantitatively analyze the impact of both exciton binding energy and intermolecular interactions on the chiroptical performances of this important family of hybrid materials.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAhn, J.; Lee, E.; Tan, J.; Yang, W.; Kim, B. \u0026amp; Moon, J. 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Commun.\u003c/em\u003e \u003cstrong\u003e14\u003c/strong\u003e, 3124 (2023).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3856748/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3856748/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eClockwise or counter-clockwise spin coating? In the current hot research topic of chiral metal-halide semiconductors, several investigations have been undertaken in order to reveal their natural optical activity and have reported dissymmetry factors (\u003cem\u003eg\u003c/em\u003e\u003csub\u003eabs\u003c/sub\u003e) for thin films of many hybrid compounds, usually without considering the macroscopic anisotropies inherent to solid-state samples. Yet, CD in the solid state can be strongly modulated by the co-existence of linear dichroism (LD) and linear birefringence (LB). Theoretical studies recently revealed the importance of such macroscopic interferences in the CD response of solid-state samples, often referred as symmetric (sLDLB) and antisymmetric (aLDLB) effects. Based on the newly synthesized one-dimensional lead-halide networks of formula (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbBr\u003csub\u003e3\u003c/sub\u003e and (\u003cem\u003eS/R\u003c/em\u003e-HP1A)PbI\u003csub\u003e3\u003c/sub\u003e, an experimental method to accurately discriminate between CD, sLDLB and aLDLB in chiral metal-halide networks is here presented. The main experimental conditions influencing sLDLB and aLDLB amplitude are also highlighted, such as the concentration of the precursor solution and the spin-coating rotation direction, finally providing a complete experimental guide for the forthcoming chiroptical investigations of such important family of chiral hybrid materials.\u003c/p\u003e","manuscriptTitle":"Experimental evidence of the molecular and macroscopic origins of circular dichroism in chiral metal-halide networks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-15 18:40:16","doi":"10.21203/rs.3.rs-3856748/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"01fa96d8-6793-4278-b911-d5cba094c2e1","owner":[],"postedDate":"March 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28448867,"name":"Physical sciences/Chemistry/Materials chemistry/Optical materials"},{"id":28448868,"name":"Physical sciences/Materials science/Materials for devices/Electronic devices"}],"tags":[],"updatedAt":"2024-07-05T07:40:33+00:00","versionOfRecord":{"articleIdentity":"rs-3856748","link":"https://doi.org/10.1002/adom.202400381","journal":{"identity":"advanced-optical-materials","isVorOnly":true,"title":"Advanced Optical Materials"},"publishedOn":"2024-05-25 07:40:33","publishedOnDateReadable":"May 25th, 2024"},"versionCreatedAt":"2024-03-15 18:40:16","video":"","vorDoi":"10.1002/adom.202400381","vorDoiUrl":"https://doi.org/10.1002/adom.202400381","workflowStages":[]},"version":"v1","identity":"rs-3856748","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3856748","identity":"rs-3856748","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}